Yes, cob is a Scrabble word!
...and is worth 7 points in Scrabble, and 9 points in Words with Friends
cob
Noun
1. Nut of any of several trees of the genus Corylus
2. Stocky short-legged harness horse
3. White gull having a black back and wings
4. Adult male swan
What Scrabble words can I make with the letters in cob?
2 Letter Words